A quietly intriguing column from the brains behind QI, the BBC quiz show. This
week: QI pigs out

No man should be allowed to be president who does not understand pigs, or hasn’t been around a manure pile.Harry S Truman

Popular pigs

There are about a billion pigs in the world at any one time, and more than half live in China, one of the first places the wild boar (Sus scrofa) was domesticated more than 9,000 years ago; to the Chinese, “meat” still means pork. Pork is the world’s most popular meat: 85 billion tons are consumed annually, a third more than beef or chicken.

Social pigs

Pig society is based around the harem: a dominant male surrounded by groups called “sounders”, each consisting of a sow and her litter, who stay together until the young come of age. Sounders continually communicate through grunts, squeaks and sniffs.

Pigs are covered in glands – feet, wrists, genitals, anus, chin, mouth, eyes – all carrying messages to their defining organ: the snout, which is approximately 2,000 times more sensitive to smell than the human nose.

Clean pigs

In terms of cleanliness, pigs are very particular. They are the only farm animals that make a separate sleeping den (which they keep spotless) and use a latrine area. They just don’t look clean.

They turn the ground more efficiently than any plough, “rooting” incessantly with their snouts. This, combined with rain, quickly leads to mud, which they use to coat themselves in as a protection against sunburn.

Sweaty pigs

If you’ve ever suggested a friend was “sweating like a pig”, you were wrong. In fact, pigs barely sweat at all. Pigs only have a few sweat glands, and to control their temperature they huddle in the cold, and pant or wallow when it gets hot.

One of the reasons for this susceptibility to temperature is their lack of brown fat, which helps most newborn mammals maintain their temperature by converting itself into heat. The UCP1 gene which controls its production was shut down in pigs’ ancestors about 20 million years ago.

The wild boar can only live in cold climates thanks to behavioural adaptations such as building a den when it is time to give birth (the only hoofed animal to do so).

Smart pigs

Pigs are highly intelligent. Like dogs, they can be easily housebroken, taught to fetch and come to heel. Pigs can learn to dance, race, pull carts and sniff out landmines.

They can even be taught to play video games, pushing the joystick with their snouts, something that even chimps struggle to master. In the 18th and 19th centuries, various “learned pigs”, dressed in natty waistcoats, travelled through Europe, amazing audiences by kneeling, bowing, spelling names with cards and “mind-reading”.

Useful pig

Every bit of a pig has a use. In 2007, Dutch artist Christian Meindertsma produced a book and an exhibition called PIG 05049, that recorded all 187 products that were derived from a single pig.

As well as high-quality leather from its skin and paint brushes from its bristles, gelatin from its skin finds its ways into liquorice, chewing gum and tiramisu. Pork fat is used in anti-wrinkle cream and shampoo and glue made from pig bones is used to reinforce matches.

Protein from pig hair is added to bread to keep it soft, and pig ashes are added to porcelain (incidentally, this is not so named for any directly piggy reason, but because of the fine ceramic body’s resemblance to the surface of a cowrie shell – these were known as porcelle, piglets, because of their shape).

Medical uses include the production of insulin and provision of replacement valves for human hearts; but you’ll also find bits of pig in beer, lemonade, car paint, brake discs, and as a coating for bullets.

Fluorescent pigs

Pig stem cells are being used to research human diseases. In order to track them once injected, Chinese geneticists have crossed a pig with a jellyfish to produce piglets whose tongues and trotters glow fluorescent green in ultraviolet light.

Piggy banks

Piggy banks used to have nothing to do with pigs. The Old English word pygg used to refer to a type of clay used for making all kinds of household objects, including pots for storing money. In Old English, pygg was used to mean “young pig”; the usual word for the adult animal was “swine”, from the Latin sus.

The Second Book of General Ignorance by John Lloyd & John Mitchinson (Faber & Faber, rrp £8.99) is available from Telegraph Books for £8.99 plus £0.99 p&p. Call 0844 871 1515 or go to books.telegraph.co.uk

The new 'I’ Series of QI is now on Fridays at 10pm and Saturdays at 9pm on BBC Two